Method and apparatus for stacking paper sheets or the like

ABSTRACT

Freshly printed paper sheets 10 issuing from the printing unit 2 of a printing machine 1 are conveyed seriatim to a position above and in registry with a collecting station 60, and are thereupon caused to descend toward the collecting station to form a growing stack 7. A stream of compressed air is blown by one or more nozzles 24 below each successive sheet in a direction from the downstream side toward the upstream side of the collecting station while the respective sheet advances toward the position of registry with the collecting station. The air stream contains comminuted solid material which deposits on the topmost sheet 12 of the stack and at the underside of each advancing sheet. Suction orifices 58 at the upstream side of the collecting station evacuate air and the surplus of comminuted material. Jets of compressed air are blown downwardly by auxiliary nozzles 32 at both sides of the path of successive sheets to assist in the generation of uniform suction in all zones of the gap 24 wherein the air stream conveys comminuted material, and to thus insure that the sheets can rapidly descend toward the collecting station without undue bulging or flexing.

D United States Patent 1 3,556,519

[72] Inventor Leo Keller FOREIGN PATENTS 7Sandaeckerstr. 38, Stuttgart-Feuerbach, 842,647 6/1952 Germany 271/86 Germany H pp No 738,067 Primary Exammer--Edward A. Sroka June 18, 1968 [45] Patented Jan. 19, 1971 [32] Priority June 23, 1967, Jan. 30, 1968, Aug. 7, 1967 [33] Germany [31] 1,536,993, 1,611,235 and 1,611,232

221 Filed [54] METHOD AND APPARATUS FOR STACKING AIt0rney-Michael S. Striker ABSTRACT: Freshly printed paper sheets 10 issuing from the printing unit 2 of a printing machine 1 are conveyed seriatim to a position above and in registry with a collecting station 60. and are thereupon caused to descend toward the collecting station to form a growing stack 7. A stream of compressed air is blown by one or more nozzles 24 below each successive sheet in a direction from the downstream side toward the upstream side of the collecting station while the respective sheet advances toward the position of registry with the collecting station. The air stream contains comminuted solid material which deposits on the topmost sheet 12 of the stack and at the underside of each advancing sheet. Suction orifices 58 at the upstream side of the collecting station evacuate air and the surplus of comminuted material. Jets of compressed air are blown downwardly by auxiliary nozzles 32 at both sides of the path of successive sheets to assist in the generation of uniform suction in all zones of the gap 24 wherein the air stream conveys comminuted material, and to thus insure that the sheets can rapidly descend toward the collecting station without undue bulging or flexing.

PATENTEUJANISIQH FIG.2

Inventor: LEO KELLER flw-zlaeff-Sn-k his ATTORNEY METHOD AND APPARATUS FOR STACKING PAPER SHEETS OR THE LIKE BACKGROUND OF THE INVENTION The present invention relates to a method and apparatus for stacking of sheets which consist of paper, cardboard, foil, plastic or the like. More particularly, the invention relates to improvements in methods and apparatus which are especially suited for stacking of paper or cardboard sheets provided with printed matter which is still wet during transport of sheets toward a collecting station. Still more particularly, the invention relates to improvements in methods and apparatus for stacking of sheets immediately after such sheets issue from a printing machine or the like so that, unless appropriate steps are taken, the matter printed thereon is likely to be smudged and/or to contaminate the adjoining sheets in response to stacking. A

it is already known to spray silicate powder onto freshly printed sheets immediately after such sheets issue from a printing machine. As a rule, the powder is sprayed at right angles to the printed surfaces of sheets by resorting to 'noules which discharge powder in admixtureto compressed air. A drawback of such procedure is that the streams of compressed air rebound on the sheets and flow in all directions beyond the edges of sheets to carry away surplus powder and to thus contaminate the stacking or collecting station and its surroundings. The surplus of powder is bothersome to attendants and deposits on moving parts of the printing machine to cause excessive wear and to necessitate frequent cleaning.

Another drawback of conventional stacking apparatus is that a cushion of air develops between the topmost sheet of the stack and the sheet which is about to be deposited on the stack. The cushion does not disappear as fast as a freshly admitted sheet can descend onto the stack. The undesirable effect of the air cushion is more pronounced with increasing size, decreasing weight and decreasing stability of sheets. As a rule, the air cushion causes deformation of sheets which are about to descend onto the stack, particularly a bulging of central portions and a flexing of the edges. This affects the uniformity of the stack. Attempts to overcome the undesirable effects of air cushions include the provision of pneumatic brakes at the end of the stack, auxiliarygrippers which engage a sheet shortly before it descends onto the topmost sheet of the growing stack, and nozzles which blow air on top of each descending sheet to force it rapidly against the topmost sheet of the stack. Such auxiliary equipment contributes significantly to the initial and maintenance cost of stacking apparatus; moreover, its effectiveness is negligible when the apparatus is employed to stack large and/or lightweight sheets, Still further, such auxiliaries fail to overcome the problems which arise due to escape of surplus protective powder into the area surrounding the sheet collecting station.

SUMMARY OF THE INVENTION LII it is an important object of the present invention to provide a novel method of stacking sheets of paper, cardboard or the like in such a way that the surplus of protective powder cannot contaminate the area surrounding the sheet collecting station, that the sheets can be stacked rapidly, that the thus stacked sheets can form a neat stack, and that the sheets undergo minimal deformation during travel toward the growing stack.

Another object of the invention is to provide a novel stacking apparatus which can be employed in the practice of the just outlined method and which insures the formation of a neat stack and prevents contamination of the area around the stack with a minimum of auxiliary equipment which is of simple design and occupies a small amount of space.

A further object of the invention is to provide an apparatus which prevents the formation of an air cushion between the topmost sheet of a growing stack and the sheet which is about to be delivered to the stack.

The improved method is employed for stacking sheets of blank or printed paper or the like at a collecting station and comprises the steps of transporting a series of sheets edgcwise along a predetermined path at least a portion of which extends above and is separated from the topmost-sheet of the growing stack at the collecting station by a gap so that each of the thus transported sheets advances toward and requires a certain interval of time to reach a position of registry with the collecting station, conveying a stream of gas across the gap between each advancing sheet and the collecting station, at least during a portion of the respective interval, and thereupon effecting downward movement of each of the series of sheets from the position of registry toward the collecting station so that each succeeding sheet comes to rest on the preceding sheet. The gas stream is preferably a stream of air which is blown between each advancing sheet and the collecting station, preferably in a direction from the downstream side toward the upstream side of the collecting station as considered in the direction of sheet advance into registry with the collecting station, i.e., the air stream is blown counter to the direction in which the sheets advance toward the position of registry. The air blowing step preferably begins when a sheet is located at a first predetermined distance and is terminated when the sheet is located at a second predetermined distance from the position of registry with the collecting station. Such stream is' preferably blown in substantial parallelism with the planes of sheets at the collecting station.

In accordance with another feature of my method. the air stream is evacuated, preferably by suction, at the upstream side of the collecting station. Silicate powder or another suita ble finely comminuted solid material can be fed into the gap between the topmost sheet of the stack and the sheet which advances toward the position of registry with the collecting station so that such comminuted material deposits at the un-' derside of the advancing sheet and at the upper side of the topmost sheet at the collecting station. At least some such comminuted material, but preferably all of the comminuted material, can be introduced into the air stream which then carried the surplus toward the upstream side of the collecting station where the surplus is evacuated and collected by suction, together with the air stream. The comminuted material can be introduced into the gas stream before the latter enters the gap between the growing stack and a sheet which advances toward the position of registry with the collecting station.

In accordance with still another feature of my method, the gap between the stack and a sheet advancing toward the position of registry with the collecting station is open at one or more sides, preferably at the two sides which are parallel with the aforementioned path, and the step of effecting downward movement of sheets toward the collecting station comprises conveying second streams of gas (preferably compressed air) along the open sides of the gap to produce with the main air stream substantially uniform suction in all zones of the gap whereby the suction insures rapid descent of each sheet from the position of registry with the collectingstation toward and onto the topmost sheet of the growing stack. At least a portion of each second stream is preferably adjustable, for example, by changing at least one of several characteristics of the respective second stream. Such characteristics include the velocity, the direction and the cross-sectional area of a second stream.

Each preceding sheet can be held, preferably by suction, against movement with reference to the collecting station, at least while the gas stream is being conveyed across the afore mentioned gap.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved stacking apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic side elevational view of a stacking apparatus which embodies the invention; and

""I-TIG. 2 is a fragmentary schematic sectional view as seen in the directionof arrows from the line II-II of FIG. 1.

. DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawing illustrates an apparatus 3 which forms part of a printing machine 1 and is utilized for stacking of paper or cardboard sheets 10 immediately or shortly after, such sheets issue from a printing unit 2 of the machine 1. The details of the printing unit 2 form no part of the present invention. This printing unit discharges a series of freshly imprinted sheets 10 which are thereupon transported by a transporting means 5 including an endless chain or belt 6 provided with longitudinally spaced elongated rodlike entraining members or grippers 9 each of which grips the front edge or leading edge of the respective sheet 10. The chain 6 has a substantially horizontal stringer or stretch 6a which defines a portion of the path along which the sheets 10 advance at a level above and toward the position of registry with a stacking or collecting station 60 releases the respective sheet 10 shortly or immediately before such sheet reaches the position of registry with the station 60.

The chain 6 is trained over a sprocket wheel 8 which is "located above the downstream side of the collecting station 60, as considered in the direction of travel of sheets 10 toward the position of registry with such station. In the illustrated embodiment, a sheet which issues from the printing unit 2 first moves upwardly, thereupon over a suction drum or flattening drum 11, and along the stretch 6a in a direction toward the sprocket wheel 8". The motor which drives the chain 6 is not shown in the drawing. The suction drum 11 is rotatable and its purpose is to stretch'or flatten a sheet 10 while such sheet advances toward the position of registry with the collecting 'staare of similar or identical design and each thereof comprises a row or line of auxiliary nozzles 32 which can blow jets of compressed air downwardly to assist thenozzles 24 to produce in the gap 14 suction which causes and-facilitates rapid and smooth descent of sheets 10 onto the topmost sheet 12 of the growing stack 7.

The nozzles 24 of the conveying device 13 are mounted on adjusting means which serves to adjust-the position of such nozzles with reference to the path along which the sheets 10 advance with the lower stretch 6a of theichain 6. Such adjusting means includes carrier means in thefor'm of legs 19 which can be moved by a drive 20 between the solid-line and phantom-line positions of FIG. 1. In the illustrated embodiment, the conveying device 13 comprises three legs 19. This device 13 further comprises an air compressor 21 or an analogous source of compressed gas which is connected with the nozzles 24 by way of a supply conduit or hose 22 containing a regulating valve 23. A second supply conduit or hose'22 branches from the supply conduit 22 upstream of the valve 23 and serves to deliver compressed air to the auxiliary nozzles 32 of the conveying devices 16 and 17. The conduit 22 contains a regulating valve 23'. Each of the conveying devices 16, 17 comprises several sets or groups of nozzles 32; FIG. -1 shows that the conveying device 17 comprises three groups 29, 30, 31 of nozzles 32. All of the nozzles 32 in the conveying device 16 or 17 areshown as being pivotable about a common horizontal axis defined by a shaft 26 which is parallel to the lower stretch 6a of the chain 6. Each of the groups 293l may but need not comprise the same number of nozzles 32. Flexible hoses 33 connect the groups 29-31 toeach other and serve to deliver compressed air from the supply coriduit 22' as well as to permit independent angular displacement of nozzles 32 in any one of the groups-29-'31-with reference to the nozzles 32 of the other group. The nozzles 32 may but need not be of identical deign and it is equally possible to mount the nozzles 32 in each of the groups 2931 for independent angular or other movement with reference to each other so as to change the characteristics of jets of compressed air which are being discharged by the orifices of such nozzles .in'order to assist the nozzles 24 to create suction in the gap 14. fit is also possible to provide the nozzles 32 with adjustable ori- I fices so that the cross-sectional areas of the respective jets can like openings or orifices which draw air and thereby attract the adjoining portions of advancing sheets. The sheets are bechanged at the will of persons in charge in order to further .tion 60. The drum 1 1 is provided with peripheral ports, slits org influence suction in the gap 14. Each of the groups 29-31 comprises a carrier 35 which is pivotable on the respective shaft 26 independently of the other carriers 35' and is biased V i by a spring 36 to bear against the face of a rotary cam 29 stretched in response to the pull produced by the respective:

grippers 9.

The aforementioned support 8 constitutes a platform or base which is movable up and down, preferably in automatic response to increasing height or weight of the stack 7, so that the topmost sheet 12 of the stack is invariably held at a predetermined level, i.e., that the height of the gap 14 .between the topmost sheet 12 and the sheet 10 advancing I ing device 13 includes a set of nozzles 24 which discharge compressed air intermittently, always while a sheet 10 is in motion and advances with the respective gripper 9 toward the .downstream end of the gap 14. The thus admitted air is withdrawn by an evacuating device 15 which is adjacent to the upstream side of the collecting station 60, Le, next to the suction drum 11.

The apparatus 3 also comprises two additional or auxiliary :conveying devices 16, 17 which are adjacent to the two open sides of the gap 14 and extend in parallelism with the stretch 6a of the transporting chain 6. The conveying devices 16, 17

which is mounted on a driven camshaft 37 (see FIG. 2). The camshafts 37 derive motionfroin the drive 20 for the legs 19 of the conveying device 13. The earns 39 have cam faces which are designed to pivot the carriers 35 independently of each other; alternatively, each of the camshafts 37 can carry a set of three cams 39, one foreach carrier 35 of the conveying device 16 or 17. The drive 20 is operatively connected with the sprocket wheel 8' by a belt or chain 40 so that its operation is synchronized with that of the transporting means 5.

At least one of the legs 19 further carries a holding means including a suction-operated holding member or cup 41 which can move into engagement with the topmost sheet 12 of the stack 7 while the nozzles 24 discharge compressed air in a direction toward the evacuating device 15. This insures that the air stream cannot'displace the topmost sheet 12. Each holding member 41 is connected with a suction pump 44 or an analogous suction generating device a suction pipe 42 which contains a regulating valve 43. A second suction pipe 47 which contains a regulating valve 48 connects the suction pump 44 with a stationary suction chamber 46 of the aforementioned evacuating device 15. The suction chamber 46 is provided with at least one row or line of suction ports or orifices 58 serving to withdraw from the gap'14 air which is being admitted by the nozzles 24. The valves 23, 23, 43, 48 are operatively connected (as at 49) with a control unit or programming unit 50 of the printing machine 1. The programming unit 50 also controls the operation of the drive for the transporting chain 6.

The operation is as follows:

When a sheet which is being pulled by the respective gripper 9 and is being flattened by the suction drum 11 reaches a predetermined distance from the position of registry with the collecting station 60, the programming unit 50 opens the valves 23, 23', 43, 48 by way of the operative connection 49. The arrangement is preferably such that the opening of valves 43, 48 precedes the opening of valves 23, 23'. When the valve 23 opens, it causes the nozzles 24 of the main conveying device 13 to admit a primary stream of compressed air which flows above and in parallelism with the topmost sheet 12 in a direction toward the evacuating device 15 and which also flows along the underside of the sheet 10 which advances along the stretch 6a. The primary stream of air which is discharged by the noules 24 carries a mass of silicate powder or other suitable finely comminuted solid material which can be used to effect rapid dusting of printed matter on the sheets 12 and/or 10. it is preferred to mix such powder with compressed air before the latter issues from the nozzles 24. This is achieved by the provision of a magazine or source 55 which contains powder and is in communication with the supply conduit 22 upstream of the nozzles 24. The magazine 55 preferably admits into the conduit 22 all of the powder which is necessary for dusting of a sheet 10 and/or 12. During discharge of compressed air into the gap 14, the legs 19 of the adjusting means in the conveying device 13 maintain the nozzles 24 in positions which are shown in FIG. 1 by solid lines, i.e., the orifices of nozzles 24 are located at a level above the topmost sheet 12 of the growing stack 7. The holding members 41 engage the topmost sheet 12 of the stack 7 and hold this sheet against movement relative to the stack during discharge of compressed air by the nozzles 24. It will be recalled that the valve 43 preferably opens slightly ahead of the valve 23 so that the holding members 41 are already connected to the suction pump 44 when the nozzles 24 begin to receive compressed air from the compressor 21. The nozzles 24 are preferably designed in such a way that the upper side of the topmost sheet 12 in the stack 7 is exposed to a turbulent air stream which flows in substantial parallelism with the sheet 12 toward the evacuating device 15, i.e., in parallelism with the rows or lines of nozzles 32 in the auxiliary conveying devices 16 and 17. The suction chamber 46 of the evacuating device 15 is adjacent to the drum 11 and its orifices or ports 58 evacuate air which is admitted by the nozzles 24 as well as any surplus of powder, i.e., all such powder which failed to adhere to the underside of the sheet 10 and/or to the upper side of the sheet 12. As mentioned before, the suction chamber 46 is connected to the pump 44 before or not later than when the nozzles 24 receive compressed air.

When the valve 23' opens in response to a signal from the programming unit 50, it admits compressed air to the nozzles 32 of the conveying devices 16 and 17. The noules 32 discharge jets of compressed air substantially downwardly to produce two curtains of air which flank the open sides of the gap 14 and assist the nozzles 24 to create in the gap a suction which prevents the formation of an air cushion. The two air curtains extend along the full length of the collecting station 60, i.e., all the way from the suction chamber 46 to the holding members 41. At the same time, the drive causes each of the two cam shafts 37 to complete a full revolution and to thus pivot the nozzles 32 by way of the corresponding carriers 35. Rotation of the cams 39 is terminated simultaneously with closing of the regulating valve 23'. The valves 23, 23', 43, 48 close when a sheet 10 is located at a predetermined distance from the position of registry with the collecting station 60. Such closing takes place before the sheet 10 actually reaches the position of registry with the station 60. The valves 43, 48 can be closed shortly after closing of the valve 23, and the valve 23' can be closed simultaneously with, ahead of, or subsequent to closing of the valve 23.

. The pneumatic components of the stacking apparatus 3 (namely, those including the nozzles 24, 32, suction chamber 46 and holding members 41) are designed in such a way that, when the nozzles 24, 32 discharge compressed air, i.e., when the valves 23 and 23 are open, such air creates substantially uniform suction in all zones of the gap 14 between the sheets 10 and .12. At the same time, the primary air stream which is discharged by the nozzles 24 insures, uniform distribution of powder on the top face of the sheet 12 as well as along the underside of the sheet 10. Uniform suction is preferably maintained until or shortly before the sheet 10 reaches a position in which it is released by the corresponding gripper 9 and has advanced beyond the suction drum 11 so that the suction effects rapid and smooth descent of the sheet 10 toward and onto the sheet 12. Such descent of the sheet 10 takes place without any bulging of its central portion. The valves 23, 23', 43, 48 are closed not later than at a time when the sheet 10 reaches the top face of the sheet 12 whereby the two sheets lie flat against each other. Suitable ,abutments or stops (not shown) can be provided at the station 60 to determine, with utmost accuracy, the final position of the sheet 10 on top of the sheet 12.

An important function of jets which are discharged by the nozzles 32 of the conveying devices l6, 17 is to insure that suction created by aii' which is discharged by the nozzles 24 is felt all the way to the open lateral sides of the gap 14. it was found that, by effecting pivotal movements of nozzles 32 about the axes of the respective shafts 26, one can further improve the manner in which a sheet 10 descends from the position of registry with the collecting station 60 toward the sheet 12 at the collecting station 60.

When the valve 43 closes, the drive 20 of the conveying device 13 causes the legs 19 to move the nozzles 24 and holding members 41 to the position shown in H6. 1 by phantom lines so that these parts cannot interfere with movement of the sheet 10 into actual abutment with the sheet 12. The drive 20 is then actuated again to return the nozzles 24 and holding members 41 to the solid-line positions of FIG. 1.

The suction drum 11 contains or is adjacent to a stationary baffle or shield (not shown) which seals from the suction pump 44 all but those suction ports which are adjacent to the sheet 10. Thus, the drum 11 does not or need not draw any air which is being blown by the nozzles 24 of the conveying device 13. As shown in H6. 2, the drum 11 is a composite drum in that it comprises a row of shorter suction drums or wheels 57 mounted on a common hollow shaft 56. The spaces between the wheels 57 accommodate portions of the suction chamber 46.

The flow of air in the conduits 22, 22' and pipes 42, 47 can be regulated by the valves 23, 23, 43, 48 and/or by additional adjusting valves which are not shown in the drawing. As stated before, the intervals during which the valves 23, 23', 43, 48 remain open may but need not be identical. Thus, the valve 48 is preferably closed subsequent to closing of the valve 23. Angular adjustability'of nozzles 32 about the respective shafts 26 renders it possible to determine the direction of jets which issue from such nozzles to pass along the open sides of the gap 14 and to influence suction in this gap. The nozzles 32 of each group can be adjusted independently of each other or two or more or all nozzles of an entire group are adjustable as a unit with reference to the nozzles of each other group.

Very satisfactory results were achieved with nozzles 24 which are designed to produce a turbulent stream of air. It is often desirable to employ in the conveying device 13 two or more types of blowing nozzles 24, preferably in such a way that the median nozzle or nozzles 24 discharge straight streams of air which flow at a high speed and with a minimum of turbulence, and that the outer nozzles 24 produce relatively wide streams of air which flow at a lesser velocity and resemble flat curtains travelling in parallelism with the sheet 12. Such outer nozzles 24 may be of the type known as air cushion nozzles. The jets of air issuing from the nozzles 32 of the conveying devices 16, 17 contribute to turbulence in air streams discharged by the nozzles 24 and thus enhance uniform distribution of powder which enters the conduit 22.

' EXAMPLE pers 9 of t'h'e chain 6 were set to advance the sheets at a speed of 2 meters per second, and such sheets consisted of paper orcardboard. The nozzles 24 discharged compressed air at a speed of -30 meters per second, and the nozzles 32 discharged jets of compressed air at a speed of 6-12 meters per second. The angle which the jets of air issuing from the nozzles 32'rnade with the .plane of the topmost sheet 12 at the collecting station 60 was 90l 10 degrees. The magazine 55 contained a supply of finely comminuted silicate powder.

It was found that the machine was capable of stacking the sheets in rapid sequence, without any flexing or bulging, and that all printed matter on the sheets was uniformly covered with powder so that the adjoining surfaces of sheets were not contaminated and the the printed matter remained clearly legible.

Certain of the important features and advantages of my method and apparatus can be summarized as follows.

The distribution of powder which is being drawn from the magazine 55 is more uniform than in presently known stacking apparatus because the powder is conveyed along the entire upper side of the topmost sheet 12 in the stack 7. Furthermore, the surplus of powder cannot contaminate the printing machine because it is withdrawn by the evacuating device 15.1

Also, the air stream discharged by nozzles 24 insures deposition of powder at the underside of an advancing sheet 10 as well as along the upper side of the topmost sheet 12 at the collecting station 60 so that the likelihood of smudging is even more remote. The air stream discharged by nozzles 24 performs several important functions, namely, it brings about uniform distribution of powder along the topmost sheet 12 and along'the underside of the advancing sheet 10, and such air stream also creates suction in the gap 14 to insure rapid and smooth descent of sheets 10 on top of the growing stack 7. Thus, the primary air stream not only improves the distribution of powder but also contributes to deposition of sheets at the collecting station. Since the powder is being conveyed in parallelism with the planes of sheets 10 and 12, it is less likely to rebound on such sheets and to escape laterally beyond the gap 114 with the danger of contamination of the printing machine. The advancing sheet 10 provides a cover for the air stream'which is discharged by the nozzles 24 and for the dispersed powder which admixed to the air stream upstream of the nozzles 24. This insures that the air stream can flow along the entire top face of the sheet 12 and that such top face is uniformly covered with powder, or that all printed matter on such top face is properly dusted prior to contact with the underside of the sheet 10. if desired, an electrostatic field can be established at a level above the stretch 6a of the chain 6 to enhance the deposition of powder at the underside of the sheet 36. However, it was found that the admission of powder into we supply conduit or conduits 22 normally suffices to insure at least some sedimentation along the underside of the sheet 10. Such sedimentation can be promoted by appropriate selection of the size, configuration and/or distribution of orifices in the nozzles 24. The drive can be used not only to move the legs 19 between the solid-line and phantom-line positions of FIG. 1 but also to change the angular position and/or to effect other movements of one or more nozzles 24 while a sheet advances toward a position of registry with the collecting station 60 to thereby further influence the distribution of powder along the sheets 10 and 12. Such movements of nonles 24-can take place simultaneously or in a predeterminedsequence. Furthermore, such movements of nozzles 24 can influence suction in the gap 14 and hence the speed and the manner in which a sheet 10 descends onto the stack 7. The distribution of powder and the suction in the gap 14 can be influenced by adjusting the position of the nozzles 24, by proper timing of the begin and termination of air discharge from these noules, by proper selection of the speed of the primary air stream, by proper selection of the interval during which the nozzles 24 discharge air, and by proper synchronization of air discharge from nozzles 24 with operation of the conveyor 5.

The nozzles 24 may be similar to those commonly used in another part of the printing machine 1 to feed sheets to the printing unit. Relatively minor alterations in the design of such conventional nozzles render them capable of performing the functions of nozzles 24 and of the holding members 41. An important advantage of holding members .41 is that they can properly hold the topmost sheet 12 without exerting undue pressure upon the stack 7. While a singlefholding member 41 might suffice, it isnormally preferred to employ a series-of two or more holding members. The same applies for the number of nozzles 24. As stated before, the nozzles 24 may be of two or more types if such different types of nozzles insure better distribution of powder in all zones of the gap'l4. The admission of air from the compressor 21 to the nozzles 24 preferably takes place at a time when the sheet 10 is sufficiently close to i the position of registry with the collecting station 60 to prevent uncontrolled escape of compressed air between the nozzles 24 and the corresponding gripper 9.

Suction in the gap 14 is created primarily by the primary air stream which is discharged by the nozzles 24 and secondarily by jets of air issuing from the nozzles 32 of the conveying devices l6, 17. The curtains ofair'produced by jets issuing from nozzles 32 provide shields at the sides of the primaryair stream and suchcurtains can be adjusted not only prior to but also during'dis'charge of jets to insure uniform suction in all zones of the gap. As mentioned hereinbefore. conventional stacking apparatus cannot prevent the formation of air cushions between the topmost sheets of a growing stack and the sheets which are about to be added to the stack. Since the cushion disappears more rapidly along the edges of the topmost sheet, the freshly admitted sheet develops a centrally located bulge and entraps a bubble of air at the top face of the preceding sheet. Such bulge creates many problems; for example, it causes extensive smudging of printed matter on contact of a bulging sheet with the next-following sheet.

The nozzles 32 may also be of the 'type known as air brushes, backfilling nozzles or the like. Adjustability -of nozzles 32, combined with the adjustability of nozzles 24, renders it possible to establish in the gap 14 conditions which are best suited to effect rapid and smooth descent of sheets onto the growing stack without the formation of bulges, air bubbles and other inconveniences. The suction created by air issuing from nozzles 24, 32 insures uniform descent of all portions of a sheet 10, i.e., also of those portions which are closely adjacent to the suction drum 11. This is achieved by insuring that such suction is maintained at least until the trailing end of the sheet 10 clears the suction drum 1 1.

Finally, it is obvious that the stacking apparatus of my invention can be used with equal advantage for transportation and controlled deposition or collection of sheets which consist of a material other than paper or cardboard. The stacking apparatus can be used with or without the magazine 55 it was found that the apparatus is particularly suited for use in offset printing and like machines.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

1 claim:

1. A method of stacking sheets of printed paper or the like at a collecting station comprising the steps of transporting a series of sheets edgewise alonga predetennined path at least a portion of which extends above and is spaced from the collecting station to bring each advancingsheet into a position of registry with the collecting station; blowing a stream of gas between each advancing sheet and said collecting station as the advancing sheet from the space between said advancing sheet and said collecting station at least during the time of conveying said stream of gas so as to prevent said stream of gas to form a gas cushion under the advancing sheet and to thus effect fast downward movement of each of said series of sheets from said position of registry towards said collecting station so that each succeeding sheet comes to rest on the preceeding sheet.

2. A method as defined in claim l, wherein said conveying step comprises blowing air between each advancing sheet and said collecting station.

3. A method as defined in claim 1, wherein said conveying step comprises blowing air between each advancing sheet and the collecting station when the respective sheet is located at a predetermined distance from said position of registry.

4. A method as defined in claim 1, wherein said conveying step comprises blowing air counter to the-direction in which the sheets advance toward said position of registry.

5. A method as defined in claim 1, wherein said conveying step comprises blowing air in substantial parallelism with the direction in which'the sheets advance toward said position of registry.

6. A method as defined in claim 1, wherein said conveying step comprises blowing air from at least one point located downstream of said collecting station as considered in the direction in which the sheets advance toward said position of registry.

7. A method as defined in claim 1, wherein the step of withdrawing the air stream is performed from at least at one point located upstream of said collecting station.

8. A method as defined in claim 1, further comprising the step of holding each preceding sheet against movement with reference to said collecting station, at least while said gas stream is conveyed between such preceding sheet and the succeeding sheet.

9. A method as defined in claim 8, wherein said holding step comprises retaining the preceding sheet by suction at the downstream side of said collecting station as considered in the direction in which the sheets advance toward said position of registry.

10. A method as defined in claim 1, wherein said conveying step is terminated when the respective sheet is located at a predetermined distance from said position of registry.

11. A method as defined in claim 1, for stacking of flexible sheets, and further comprising the step of conveying at least one auxiliary gas stream along the path of said first mentioned gas stream so as to produce substantially uniform suction between each advancing sheet and said collecting station and to thus prevent excessive flexing of sheets prior to and during downward movement of sheets toward said station.

12. A method as defined in claim 1, further comprising the step of feeding finely comminuted solid material between said path and said collecting station so that such material deposits on sheets advancing along said path as well as on the topmost sheet at said collecting station.

13. A method as defined in claim 12, wherein said feeding step comprises introducing at least some of said comminuted material into said gas stream so that such stream carries the comminuted material along the sheet advancing toward said position of registry and the topmost sheet at said collecting station.

14. A method as defined in claim 13,-wherein all of said comminuted material is introduced into said gas stream.

15. A method as defined in claim 14, wherein said gas stream is mixed with comminuted solid material prior to admision between said path and said collecting station.

16. A method as defined in claim 12, wherein said comminuted material is fed in quantities exceeding those which accumulate on sheets flanking said gas stream, and further comprising the step of evacuating the surplus of comminuted material by suction before the respective sheet reaches said position of registry.

17. A method for stacking sheets of printed paper or the like at a collecting station comprising the steps of transporting a series of sheets edgewise toward a position of registry with the collectingstation along a predetermined path at least a portion of whichextends above the collecting station and is separated therefrom by a gap having at least one open side;

blowing a stream of gas across said gap; andconveying asecond stream of gas along said open side in a direction having at least one component which is normal to the plane of the lower surface of said gap so as to produce substantially uniform suction in all zones of said gap to thus effect fast downward movement of each of said series-of sheets from the position of registry towards said collecting stationso that each succeeding sheet comes to rest on the preceding sheet.

18. A method as defiried in claim 17, wherein said gap has two open sides extending in parallelism with the direction in which the sheets advance toward said position of registryQsaid further step comprising conveying a second stream of gas along each open side of said gap.

1 19. A method as defined in claim 17, further comprising the step of adjusting at least a portion of said second stream.

20. A method as defined in claim 19, wherein said adjusting step comprises changing at least one of a series of characteristics of said portion of the second stream including the velocity, direction and cross-sectional area of said last named portion. 7

21. A method as defined in claim 17, wherein the second stream of gas is conveyed substantially transversal to the plane of the upper surface of the .collecting station, the second stream is passing the'open side of the gap from above down.

22. In an apparatus for stacking sheets of printed paper or the like, a combination comprising support means defining a collecting station; transporting means for moving a series of sheets edgewise along a predetermined path at least a portion of which extends above and is spaced from said support means so that each of the thus transported sheets advances towards and requires an interval of time to move into registry with said collecting station; and conveying means for conveying a gas stream between each advancing sheet and said collecting station, at least during a portion of the respective interval, said conveying means comprising at least one nozzle arranged to discharge a stream of compressed gas at a level above and to one side of said collecting station and means for withdrawing said gas stream from the opposite side of said collecting sta tion.

23. A combination as defined in claim 22, further comprising adjusting means for changing the position of said nozzle with reference to said path.

24. A combination as defined in claim23, wherein said adjusting means comprises movable carrier means connected with said nozzle and drive means for moving said carrier means.

25. A combination as defined in claim 24, wherein the sheets reaching said position of registry are permitted to descend toward and to accumulate on top of each other at said collecting station to form a stack, and further comprising holding means provided on said carrier means and arranged to hold the topmost sheet of said stack against movement with reference to said support means while said nozzle admits a gas stream between such topmost sheet and a sheet advancing along said path.

26. A combination as defined in claim 25 wherein said holding means comprises at least one suction-operated holding member.

27. A combination as defined in claim 22, wherein said portion of said path is separated from said collecting station by a gap having at least one open side and wherein said nozzle discharges compressed air into said gap, and further comprising second conveying means for conveying a second gas- 29. A combination as defined in claim 25, wherein said gap has two open sides extending in parallelism with the direction in which the sheets advance toward said position of registry, and wherein said second conveying means comprises two rows of nozzles each arranged to discharge jets of compressed air along one side of said gap.

3 05A combination as defined in claim 29, wherein said first mentioned nozzle is located at the downstream side of said collecting station as considered in said direction and is arranged'to blow said stream of compressed gas in substantial parallelism with said portion of said path and counter to said direction. 

1. A method of stacking sheets of printed paper or the like at a collecting station comprising the steps of transporting a series of sheets edgewise along a predetermined path at least a portion of which extends above and is spaced from the collecting station to bring each advancing sheet into a position of registry with the collecting station; blowing a stream of gas between each advancing sheet and said collecting station as the advancing sheet from the space between said advancing sheet and said collecting station at least during the time of conveying said stream of gas so as to prevent said stream of gas to form a gas cushion under the advancing sheet and to thus effect fast downward movement of each of said series of sheets from said position of registry towards said collecting station so that each succeeding sheet comes to rest on the preceeding sheet.
 2. A method as defined in claim 1, wherein said conveying step comprises blowing air between each advancing sheet and said collecting station.
 3. A method as defined in claim 1, wherein said conveying step comprises blowing air between each advancing sheet and the collecting station when the respective sheet is located at a predetermined distance from said position of registry.
 4. A method as defined in claim 1, wherein said conveying step comprises blowing air counter to the direction in which the sheets advance toward said position of registry.
 5. A method as defined in claim 1, wherein said conveying step comprises blowing air in substantial parallelism with the direction in which the sheets advance toward said position of registry.
 6. A method as defined in claim 1, wherein said conveying step comprises blowing air from at least one point located downstream of said collecting station as considered in the direction in which the sheets advance toward said position of registry.
 7. A method as defined in claim 1, wherein the step of withdrawing the air stream is performed from at least at one point located upstream of said collecting station.
 8. A method as defined in claim 1, further comprising the step of holding each preceding sheet against movement with reference to said collecting station, at least while said gas stream is conveyed between such preceding sheet and the succeeding sheet.
 9. A method as defined in claim 8, wherein said holding step comprises retaining the preceding sheet by suction at the downstream side of said collecting station as considered in the direction in which the sheets advance toward said position of registry.
 10. A method as defined in claim 1, wherein said conveying step is terminated when the respective sheet is located at a predetermined distance from said position of registry.
 11. A method as defined in claim 1, for stacking of flexible sheets, and further comprising the step of conveying at least one auxiliary gas stream along the path of said first mentioned gas stream so as to produce substantially uniform suction between each advancing sheet and said collecting station and to thus prevent excessive flexing of sheets prior to and during downward movement of sheets toward said station.
 12. A method as defined in claim 1, further comprising the step of feeding finely comminuted solid material between said path and said collecting station so that such material deposits on sheets advancing along said path as well as on the topmost sheet at said collecting station.
 13. A method as defined in claim 12, wherein said feeding step comprises introducing at least some of said comminuted material into said gas stream so that such stream carries the comminuted material along the sheet advancing toward said position of registry and the topmost sheet at said collecting station.
 14. A method as defined in claim 13, wherein all of said comminuted material is introduced into said gas stream.
 15. A method as defined in claim 14, wherein said gas stream is mixed with comminuted solid material prior to admission between said path and said collecting station.
 16. A method as defined in claim 12, wherein said comminuted material is fed in quantities exceeding those which accumulate on sheets flanking said gas stream, and further comprising the step of evacuating the surplus of comminuted material by suction before the respective sheet reaches said position of registry.
 17. A method for stacking sheets of printed paper or the like at a collecting station comprising the steps of transporting a series of sheets edgewise toward a position of registry with the collecting station along a predetermined path at lEast a portion of which extends above the collecting station and is separated therefrom by a gap having at least one open side; blowing a stream of gas across said gap; and conveying a second stream of gas along said open side in a direction having at least one component which is normal to the plane of the lower surface of said gap so as to produce substantially uniform suction in all zones of said gap to thus effect fast downward movement of each of said series of sheets from the position of registry towards said collecting station so that each succeeding sheet comes to rest on the preceding sheet.
 18. A method as defined in claim 17, wherein said gap has two open sides extending in parallelism with the direction in which the sheets advance toward said position of registry, said further step comprising conveying a second stream of gas along each open side of said gap.
 19. A method as defined in claim 17, further comprising the step of adjusting at least a portion of said second stream.
 20. A method as defined in claim 19, wherein said adjusting step comprises changing at least one of a series of characteristics of said portion of the second stream including the velocity, direction and cross-sectional area of said last named portion.
 21. A method as defined in claim 17, wherein the second stream of gas is conveyed substantially transversal to the plane of the upper surface of the collecting station, the second stream is passing the open side of the gap from above down.
 22. In an apparatus for stacking sheets of printed paper or the like, a combination comprising support means defining a collecting station; transporting means for moving a series of sheets edgewise along a predetermined path at least a portion of which extends above and is spaced from said support means so that each of the thus transported sheets advances towards and requires an interval of time to move into registry with said collecting station; and conveying means for conveying a gas stream between each advancing sheet and said collecting station, at least during a portion of the respective interval, said conveying means comprising at least one nozzle arranged to discharge a stream of compressed gas at a level above and to one side of said collecting station and means for withdrawing said gas stream from the opposite side of said collecting station.
 23. A combination as defined in claim 22, further comprising adjusting means for changing the position of said nozzle with reference to said path.
 24. A combination as defined in claim 23, wherein said adjusting means comprises movable carrier means connected with said nozzle and drive means for moving said carrier means.
 25. A combination as defined in claim 24, wherein the sheets reaching said position of registry are permitted to descend toward and to accumulate on top of each other at said collecting station to form a stack, and further comprising holding means provided on said carrier means and arranged to hold the topmost sheet of said stack against movement with reference to said support means while said nozzle admits a gas stream between such topmost sheet and a sheet advancing along said path.
 26. A combination as defined in claim 25, wherein said holding means comprises at least one suction-operated holding member.
 27. A combination as defined in claim 22, wherein said portion of said path is separated from said collecting station by a gap having at least one open side and wherein said nozzle discharges compressed air into said gap, and further comprising second conveying means for conveying a second gas stream along the open side of said gap.
 28. A combination as defined in claim 27, wherein said gas streams produce suction in said gap and further comprising adjusting means for said second conveying means to facilitate establishment of substantially uniform suction in all zones of said gap.
 29. A combination as defined in claim 25, wherein said gap has two open sides extendiNg in parallelism with the direction in which the sheets advance toward said position of registry, and wherein said second conveying means comprises two rows of nozzles each arranged to discharge jets of compressed air along one side of said gap.
 30. A combination as defined in claim 29, wherein said first mentioned nozzle is located at the downstream side of said collecting station as considered in said direction and is arranged to blow said stream of compressed gas in substantial parallelism with said portion of said path and counter to said direction.
 31. A combination as defined in claim 22, wherein said nozzle is arranged to blow compressed gas in substantial parallelism with said portion of said path and counter to the direction of sheet advance toward said position of registry, said withdrawing means comprising means for evacuating said gas by suction at the upstream end of said station as considered in said direction.
 32. A combination as defined in claim 22, further comprising means for admitting comminuted solid particulate material into said gas stream. 